Vitreous enameled products



Patented Feb. 22, 1938 UNITED STATES PATENT OFFICE mesne assignments,

to Monsanto Chemical Company, a corporation of Delaware No Drawing.

10 Claims.

This invention relates to a vitreous enameled product. It furthermore relates to an improved ferrous base alloy suitable for use in the manufacture of vitreous enameled products.

One object of the present invention is the provision of an enameled product having increased strength at elevated temperatures. Another object is the provision of an enameled product providing increased resistance to chipping of the enamel layer. A further object is the provision of an enameled sheet having increased resistance to deflection and warpage both at enameling temperatures and at ordinary temperatures. Still another object of this invention is the provision of an improved ferrous base alloy suitable for use in the manufacture of vitreous enameled objects. Other objects and advantages of my invention will become apparent from the following description and claims. In the art of enameling sheet iron and sheet steel the various ground and cover coats are fired in continuous or box type furnaces at temperatures ranging from a minimum of about 1400" F. to a maximum of about 1650 F. The base metal is therefore heated to these temperatures at which its strength is comparatively low. Small articles.either drawn or stamped from sheet may through their design promote sumcient rigidity to withstand deformation, but mas- 30 sive articles such as panelings, refrigerator linings and shells, table tops, stove parts and other related articles do not offer suflicient rigidity .through design and therefore introduce diflicult Enameling Enamellng Ordinary iron steel Constituent Steel Enameling iron may at times contain as much Application October 5, 1936, Serial No. 104,063

as 0.10 to 0.3% manganese to eliminate susceptibility to red-shortness and to lower production costs.

It is general knowledge that enameling iron afiords fewer defects and rejectionson enamel- 5 ing principally because of its lower carbon content. Its lower strength on the other hand makes it. more apt to warp and sag unless supported well during enameling. In contrast, the enameling steels are stronger at room temperatures, though not materially stronger at the enameling temperatures, and are more prone to contain defects in the enameled surface. Moreover, the steels pass through an eutectoid transformation which marks the beginning of the change from alpha to gamma iron. This transformation, the A1 arrest, or the lower critical, occurs in the usual commercial steels at close to 1340" F. The conversion of alpha to gamma iron involving large. volume changes is completed at the upper critical or the A: arrest temperature. Commercial enameling iron, due to its relative freedom from carbon has no A1 arrest. It changes to gamma iron at what is virtually the A1 arrest for pure iron. This is at 1670 F., a temperature above 26 that normally used in enameling; hence the gamma transformation may not occur on firing enameling iron. I

The A3 arrest for enameling steels varies from 1670 F. for those of low carbon to 1340 F. for 30 those of eutectoid steel compositions. It is evident from this and from the fact that the conversion begins at above 1340 F. that part or all of the alpha iron will be transformed to gamma iron on heating and that this gamma iron must revert to alpha iron on cooling from enameling temperatures. A marked contraction in volume occurs during the transformation on heating; an equally marked expansion occurs during the transformation on cooling with the result that in vitreous enameling of steels no adequate provision for supporting the articles against the above mentioned volume changes can be provided for and the finished articles are subjected to considerable distortion and warpage.

While the resistance to sagging of enameling iron has improved through the development of enamels of lower maturing temperatures, an improvement in the resistance of enameling steels to the warpage and distortion arising from contraction and expansion during phase changes cannot be accomplished as readily by the same procedure. V

I have now found that the resistance to warpage and distortion is greatly improved by alloymg the enameling sheet with phosphorus. Furthermore, I have found that the strength of enameling sheet at high temperatures is improved by phosphorus; and therefore its resistance to sagging is improved. I have also discovered that phosphorus does not enhance such common defects encountered in enameling iron or steel as copper heading, blistering, reboiling and fishscaling, nor does it aflect the adherence or bonding qualities of enamels when its content is under 0.40%. I have also discovered that resistance to chipping of the-enamel is also augmented through strengthening the base metal.

I have employed as much as 1% phosphorus in enameling sheet with excellent results. As the adherence or bond of the enamel to the base metal was somewhat less at phosphorus contents above 0.40% I have preferred to use phosphorus contents ranging from-0.1% .to 0.35% in sheet requiring good enamel adherence. The enameling stockcontaining more than 0.4% phosphorus, because of its strength and stiffness, is better suited for flat panels and for ware requiring no severe deep drawing operations as.

well as for ware in which the 'requirement'for exceptionally good enamel adherence is unimportant.

The strengthening eflect of phosphorus in steel at normal testing temperatures has been recog- ,nized for some time. Tensile properties of phosphorus bearing 22 gauge enameling iron and steel The sheet was normalized before testing.

sheet as set forth in the accompanying table illustrate this point. The enameling iron contained 0.01 to 0.02% carbon, 0.05 to 0.06% manganese, 0.02 to 0.01% silicon, about 0.03% sulphur, and phosphorus as shown in the table. The enamelingsteel contained 0.12 to 0.13% carbon, 0.08 to 0.10% silicon, 05-06% manganese, and about 0.04% sulphur, with phosphorus as shown.

Type of Tensile Yield Elongation enameling m strength strength in 2" shoot P P lbsJsq. in. lbs/sq. in. percent 0. M8 42, M an, M 32 0. 10 49, too 46, (I!) I!) 0. I) 57, (I!) k 52 (I!) 20 0. so 04, M (I!) as 0.49 71,500 62, 500 22 0. s1. aoo 73. (III 17 l. 07 91, 000 83, (I!) 14 0. (KB 53, M 42, (XI) 2o 0 17 04, 500 40, 500 21 0. 31 75, (XX) 49, ill) 21 -It is evident from the listed properties that phosphorus from the standpoint of strength is as effective as carbon. In other respects it is more satisfactory than carbon. Carbon, for example,

does not improve the strength at elevated tem-,

peratures to the same extent as phosphorus. It

likewise the A; arrest temperature which causes more alpha iron to transform during firing.

' Carbon also increases the number of such defects as blistering, rebelling nd copper heading in the enameled surface.

Phosphorus, on the other hand, improves the high temperature tensile properties and raises the A; arrest temperature of both enameling iron and steel. In the case of enameling steel 0.2 to 0.3% orus so eilectively reduces the amount of alpha iron that is converted during firing ofthe enamel as to virtually eliminate the distortion rand'warpage which prevail as a result of this conversion when steel is enameled. Moreover, phosphorus does not intensify the occurrence of common defects appearing in enameled ware. I

1670 F., 1780" It, and 1950' found it advantageous, therefore, to employ phosphorus wherever high strength andexoellent enameling qualities in sheet are desired.

My invention, therefore, embraces an improved enameling iron and steel of superior strength at room and at elevated temperatures and of superior resistance to sagging, distortion and warping. In accomplishing these improvements I alloy from 0.10% to 1% phosphorus to the iron and steel; For ordinary purposes the quantity of phosphorus is below 0.35%. and above 0.10%. Where exceptional strength is required in enameled ware I may employ more than 0.35% phosphorus and in fact increase the phosphorus to a' maximum of 1%.

The general accepted maximum percentage of phosphorus in vitreous enameling sheet is 0.04% yet most sheet-makers prefer to keep it under 0.02%. For large vitreous enameled parts where flatness of the finished part is of importance an extra low-metalloid, open hearth steel graded as.

special vitreous enameling sheet is being used. It retains its'flatness under firing better than normal steel and it gives better enameling results.

This sheet, which may be classified as enameling tion of flatness on firing, by providing a more suitable base-metal for the more brilliant and more permanent higher melting point enamels, and by increasing the temperature of the upper critical point, All theseare accomplished without detriment to enameling qualities provided the phosphorus is below 0.40%.

In steel, phosphorus is particularly advantageous from another score since it raises the A's arrest temperature to a point where the inversion of alpha to gamma iron becomes of little importance insofar as producing much distortion and warpage in the enameled article. The A;

arrest temperature on heating a steel with 0.15-

0.20% carbon and 0.03% phosphorus was 1540 I". This was raised to 1595 F. on increasing the phosphorus to 0.1%. to 1650 F. on increasing the phosphorus to 0.2% and to 1700 F. on increasing the phosphorus to 0.29%. Thus the marked rise in temperature of the A: arrest with anincrease in phosphorus content is apparent;

This rise in the A1 arrest temperature result- .ing from the addition of phosphorus is also of mark'edimportance in enameling irons containing manganese. Each 0.01% manganese reduces the A3 arrest temperature about 2.5 P. so that with 0.1 to 0.3% manganese in enameling iron its A; arrest temperature may be from 25 to F. lower than it is for iron of low manganese content. The reduction is sufllcient to bring the arrest temperature below the maximum enamel mam temperature and hence sufilcient' to promote the alpha-gamma transformation during the firing of refractory enamels. The A: at

. rest temperatures for enameling iron containing 0.004%, 0.11%, and 0.20% phosphorus were 1"., respectively.-

In a previous application, Serial .No. 81,338, filed May 22, 1936, I have shown the strength ening efiect of phosphorus in iron and steel for service at elevated temperatures. Inthis respect 5 it is superior to carbon. As aresult of alloying phosphorus to enameling iron and-steel I have found the increase in strength at elevated temperatures is reflected in greater resistance of sheet to sagging; This was demonstrated by enameling 4" by 10" specimens of 22 gauge sheet which were coated with 9.8 to 11.8 grams of round coat enamel and fired at 1580" F. for 4 minutes. They were supported on the ends leaving an unsupported span of 3% inches in the center free to sag.- The deflections after firing provided a measure of the resistance to sagging. In

a series of enameling irons containing from 0.005% to 0.40% phosphorus these measured permanent deflections were as follows:

Phosphorus oon- Permanent deflection in tent in percent inches 0. 40 +0. 02 (arched upward) The reduction in sagging as shown by these tests is due to the phosphorus content of the sheet and to the influence of phosphorus on high temperature strengths of sheet.

An enameling steel such as I prefer to use for the manufacture of enameled sheets may have 35 the following composition, where enamel adherence is not of major importance:

, Percent Phosphorus between.. 0.10 and 1.0 Carbon. do 0.01 and 0.25 Silicon do 0.01 and 0.10- Manganese do 0.02 and 0.55 Sulphur do 0.01 and 0.05 Iron Balance Where enamel adherence is of importance I prefer to use between 0.10 and 0.40% of phosphorus in a steel which otherwise has an. analysis as given above.

An enameling' iron suchas I prefer to use for the manufacture of enameled sheets may have 50 the following composition where enamel adherence is not of major importance:

- Percent Phosphorus "between" 0.10 and 1.0 Carbo do 0.01 and 0.035 55 Silicon} do 0.01 and 0.07

Manga ese do 0.02v and 0.30, Sulphur do 0.01 and 0.05 Iron Balance Where enamel adherence is of importance I prefer to use between 0.10 and 0.40% of phoscontaining the usual impurities ordinarily oc-v curring in enameling steel.

2. A vitreous enameled article comprising a layer of vitreous enamel vitrified upon the surface of a steel sheet, said steel containing 0.1%

to 1.0% of phosphorus, 0.01 to 0.25% carbon, 0.01 to 0.10% silicon, 0.02 to 0.55% manganese, 0.01

to 0.05% sulphur, the remainder being substantially iron.

3. A vitreous enameled article comprising a layer of vitreous enamel vitrified upon the surface of an iron sheet, said iron sheet containing from 0.1 to 1.0% of phosphorus, 0.01 to 0.035% carbon, 0.01 to 0.07% silicon, 0.02 to 0.30% manganese, 0.01 to 0.05% sulphur, the remainder being substantially iron.

4. A vitreous enameled article comprising a layer of vitreous enamel vitrified upon the surfaceof a steel sheet, said steel containing from 0.1 to 0.35% phosphorus, 0.01 to 0.25% carbon, 0.01 to 0.10% silicon, 0.02 to 0.55% manganese, and 0.01 to 0.05% sulphur, the balance being substantially iron.

5. A vitreous enameled article comprising a layer of vitreous enamel vitrified upon the surface of an iron sheet, 'said iron containing from 0.1 to 0.35% phosphorus, 0.01 to 0.035% carbon, 0.01 to 0.07% silicon, 0.02 to 0.30% manganese, 0.01 to 0.05% sulphur, the remainder being substantially iron.

6. A vitreous enameled article comprising a coating of vitreous enamel, vitrified upon the surface of a ferrous alloy sheet, said sheet containing from 0.1 to 1.0% phosphorus, 0.01% to 0.25% carbon, 0.01 to 0.10% silicon; 0.02% to 0.55% manganese and 0.01 to 0.05% sulfur alloyed therewith, the balance being substantially iron.

7. A vitreous enameled article comprising a layer of vitreous enamel vitrified upon the surface of a steel sheet, said steel containing sufiicient phosphorus alloyed therewith toraise the upper critical temperature of said steel above the maturing temperature of said vitreous enamel.

8. A vitreous enameled article comprising a layer of vitreous enamel vitrified upon the surface of an iron sheet, said iron containing between 0.01% and 0.25% carbon together with the usual alloying elements in iron sheets employed for enameled articles and containing, in addition,

suflicient phosphorus alloyed with said iron to V raise the upper critical temperature of said iron to above the maturing temperature of said enamel.

9. A vitreous enameled article comprising a layer of vitreous enamel vitrified upon the surface of a steel containing between 0.01% and 0.25% carbon together with the usual alloying elements and impurities in steel sheets employed for enameled steels, and containing, in addition,

sumcient phosphorus alloyed therewith to raisethe upper critical temperature of said steel to above the maturing temperature of said enamel. 10. A vitreous enameled article possessing an extended plane surface comprising a layer of vitreous enamel vitrified upon the surface of a ferrous alloy in sheet form containing from 0.01 to 0.25% carbon and containing in addition sufflcient phosphorus alloyed therewith to retain said plane surface substantially without sagging or warping, at temperatures approximating the maturing temperature of the said enamel.

DANIEL n. muss. 

